1. Field of Invention
The present invention relates to a mold for in-mold decoration which allows a low price and a short delivery period to be realized in mold manufacture, and which is excellent in thermal efficiency in its molding process.
2. Description of the Related Art
Conventionally, as a method for decorating a surface of a molded article made of resin, there has been an in-mold decoration method including the steps of continuously feeding a printed or otherwise worked decorating film into a mold, and integrating the printed layer with the molded article surface by resin pressure and heat in the molding process. The mold for in-mold decoration is a so-called mold base, which is a standardized item for mold-parts supply manufacturers. The mold base is used according to standard types for general molding-use metal molds, where a molding-use cavity is formed on mold release surfaces (parting surfaces) of the mold base. More specifically, the cavity is formed, in many cases, in such a manner that opposed surfaces of a movable-side mount 57 and a stationary-side mount 60 are recess-machined, which is a machining to provide so-called pockets 62 (see, e.g., Japanese unexamined patent publication No. 2001-1376; see FIGS. 1 and 2 thereof), respectively. Nests 53, 54 are fitted into the pockets 62 so that a parting surface is formed by these nests 53, 54 and surrounding walls of the pockets (see FIGS. 24A, 24B).
In conventional molds 51, 52 for in-mold decoration, the pockets 62, into which the nests 53, 54 are to be loaded, are recessed so that bottom portions of the pockets provided on the side mounts 57, 60 are difficult to machine with high precision, making it quite hard to parallelize opposed surfaces of the movable-side nest 53 and the stationary-side nest 54 to each other when they are loaded to the pockets 62. If the opposed surfaces of the nests 53, 54 cannot be parallelized to each other sufficiently, resin fins occur in resulting molded articles, or discharge failure of air and gas attributed to a decorating film being interposed in the molds would cause products to suffer such problems as film wrinkles and ink blots. Further the nests 53, 54 would collide upon mold clamping and become damaged.
To prevent such problems, it would be necessary to take sufficient time to machine the pockets 62 with high precision, but this would make it impossible to meet short delivery periods required in mold manufacture. Also, taking more time to do the pocket machining would cause the manufacturing cost of the molds to increase proportionally.
Moreover, the minimum dimensions required for the nests 53, 54 must be changed depending on changes in the number or size of the molded articles to be molded at a time. However, in the conventional mold for in-mold decoration, the nests 53, 54 and the pockets 62 have to be formed so as to be congruous with each other. Therefore, each time the dimensions of the nests 53, 54 are changed, it is necessary to prepare mold constituent members (mounts) having pockets suited to the nests 53, 54 of new dimensions. Indeed, a larger and fixed dimensioned pocket for the mold base would make it possible to use mold constituent members other than the nests 53, 54. In this case, the nests 53, 54 would have to be dimensioned in suitability to the size of a relatively larger pocket 62, where unnecessary parts would be included, involving wasteful material use for the nests 53, 54. Also, since the decorating film 13 would have to be dimensioned in suitability to the size of the nests including the unnecessary parts, a pattern pitch of design patterns provided on the decorating film in the film feed direction and in an across-the-width dimension of the decorating film would need to be increased, resulting in increase in wasteful use of the decorating film.
Also, since the nests 53, 54 are fitted within the pockets 62, there occurs heat conduction from the side faces of the nests 53, 54 to surrounding walls 56, 66 of the pockets on the movable-side mount 57 and the stationary-side mount 60, resulting in poor thermal efficiency of the molds 51, 52. As a result, a longer molding cycle is required. Further, since temperature control for the molds 51, 52 becomes difficult, there are considerable influences exerted on the fluidization, solidification, shrinkage, crystallization, and the like of the molten resin material. The influences extend to various aspects of performance of the molded article such as the strength, surface property, shrinkage amount, warpage, torsion, or other deformations of the molded article.
Further, although it is important in the molding process to replace the air in the cavity, the sprue, and the runner with resin material in short time and to discharge the gas that has been brought in by the resin material, the nests 53, 54 are fitted into the pockets 62 so that the surrounding walls 56, 66 constituting the pockets hinder smooth discharge during the air ventilating and gas ventilating. As a result, there would occur gas burns or wrinkles on the decorated molded article, which might cause occurrence of close contact failure between the decorating film 13 and the molded article.
Further, since the surrounding walls 56, 66 of the pockets and the nests constitute parting faces which come into contact with each other in the state that two molds are closed, a mold clamping force is applied to the decorating film interposed in between both the molds, thereby damaging the decorating film. Further, in the case where the bottom surfaces of the pockets are not machined with high precision, appropriate positioning of the nests is hard to achieve and, therefore, corner portions of the surfaces of the nests may be brought into contact with the decorating film, causing the decorating film to break.
Therefore, an object of the present invention is to provide a mold for in-mold decoration which solves the above-described issues, allows a low price and a short delivery period to be realized in mold manufacture, and contributes to stable mass production in its molding process.